Thyratron and circuit therefor



Sept. 20, 1966 P. HIRSHFIELD THYRATRON AND CIRCUIT THEREFOR- Filed Aug. 17, 1962 A TTO R NE PS United States Patent 3,274,438 THYRATRON AND CIRCUIT THEREFOR Philip Hirshfield, Passaic, N.J., assignor to Tung-Sol Electric Inc., a corporation of Delaware Filed Aug. 17, 1962, Ser. No. 217,724 Claims. (Cl. 315-406) This invention relates to a thyratron and its associated circuit with means for deionizing portions of the space within the thyratron envelope to permit faster pulse operation. The invention has particular reference to a thyratron discharge tube employed in an ignition circuit for passing heavy currents intermittently.

The discharge device described herein has been designed specifically to pass large currents, up to fifty amperes, in a very short time during a duty cycle. At other times during the cycle the tube must not pass current even though the voltage across its anode-cathode circuit is increased to a considerable value, about 2000 volts. While this tube and circuit have been used principally in an ignition circuit, it is obvious that the same type of tube and circuit can be applied to other discharge circuits such as used in conjunction with high intensity flash lamps and certain forms of computer circuits. Ignition circuits of the general type described herein have been described in detail in US. Patent 3,032,684, issued May 1, 1962, to James Kuykendall, and Patent 3,032,685, also issued May 1, 1962, .to Donald Loomis.

Modern ignition systems used on automobiles generally employ a high voltage transformer in connection with a pair of breaker points which sequentially make and break the primary current and thereby produce a series of high voltage secondary pulses which are applied to spark plugs in the engine cylinders and explode the combustible gases. There are many disadvantages to such a system especially when the combustible gases are compressed by the piston to a high pressure. Under these conditions the spark plug voltage must be raised to a value which makes it difiicult for generation by the usual system. Also, when the spark plugs develop a relatively low resistance it is very difiicult to produce a spark at all.

The present system described herein is capable of not only producing very high output voltages but also produces an output voltage pulse which has a very high rise time and for this reason is not influenced to a great degree by the leakage resistance of the spark plug. Prior ignition systems as described and claimed in the above two mentioned patents are limited to a certain degree by the speed of the discharge cycle. When this frequency, and the engine speed approach a speed which corresponds to 100 miles per hour in an eight cylinder engine, the gas within the thyratron discharge device does not deionize fast enough to permit a complete charge of the storage capacitor for the next cycle. The present circuit corrects this difficulty and sweeps away the ionized gas from the main discharge path and permits the charging cycle to proceed at a fast rate.

One of the objects of this invention is to provide an improved thyratron and circuit which avoids one or more of the disadvantages and limitations of prior art arrangements.

Another object of the invention is to increase the speed of an intermittent charge-discharge circuit.

Another object of the invention is to deionize the space between a cathode and an anode in a gaseous discharge device.

Another object of the invention is to prevent an unwanted discharge between a main cathode and an anode before the anode is fully charged by an external circuit.

Another object of the invention is to reduce the grid voltage of a discharge device to a negative potential as soon as the main discharge device has been started.

The invention comprises a thyratron and its associated circuit and includes a gaseous discharge device having the usual anode, cathode and firing electrode with an additional auxiliary anode positioned adjacent to the cathode. The charging circuit for the thyratron includes a source of electric power, a diode rectifier, a storage ca pacitor, and a coupling circuit connected to a load. The circuit also includes a discharge connection for discharging the storage capacitor through the coupling circuit and the anode-cathode circuit of the discharge device. A firing circuit for starting conduction within the discharge device includes circuit means in series with a capacitor for impressing a positive voltage on the firing electrode. The auxiliary anode is connected to a circuit which in cludes a resistor and a portion of the firing circuit, The auxiliary anode switches the discharge from the main anode and thereby deionizes the gas between the main anode and the cathode.

For a better understanding of the present invention, together with other and further objects thereof, reference is made to the following description taken in connection with the accompanying drawings.

FIG. 1 is a cross sectional view of the thyratron discharge device showing the internal construction of the electrodes.

FIG. 2 is a cross sectional view of the device shown in FIG. 1 and is taken along line 2-2 of that figure.

FIG. 3 is a schematic diagram of connections showing the thyratron connected in a typical circuit.

FIG. 4 is a graph showing some of the relationships between the anode and grid voltages.

Referring now to FIGS. 1 and 2, the discharge device comprises a sealed envelope 10 containing a gas at reduced pressure. At one end of the envelope an anode lead-in conductor 11 is sealed in the envelope and is connected to a cylindrical anode 12 which may be made of graphite. The anode is generally surrounded by a hollow cylindrical shield 13 which is open at the bottom and permits a discharge to take place through its open end. At the other end of the envelope a plurality of lead-in conductors 14 are sealed into a button-type base 15. Two of these lead-in conductors are connected to a cathode cup 16 which contains a mixture of salts which have electron emissive properties. Just above the cathode 16- is a control electrode or firing grid 17 which is a hollow cylinder and disposed in axial relationship to both the anode and cathode. The cathode and firing electrode are held in position by an insulator sleeve 18 which surrounds both of these electrodes. The sleeve is formed with a pluraliy of holes 20 positioned between the top surface of the cathode and the bottom surface of the firing electrode. These holes permit the escape of incandescent gases dur ing the conduction period and help relieve the pressure Within the cathode space.

An extra lead-in conductor 14a is sealed in the base 15 and extends only a short distance above the interior surface of the base. This extra conductor is connected as an auxiliary anode and is the novel addition to the thyratron discharge device, the other portions of this device being well known in the art.

Referring now to FIG. 3, the discharge device 10 is shown connected in a circuit which includes a storage capacitor 22, the primary winding 23 of an output transformer 24, and a series rectifier diode 25. These components represent the charging circuit of the device and the storage capacitor is charged by the application of a positive pulse connected across terminals 26 and 27. Terminal 27 is generally grounded. The discharge circuit of this arrangement comprises the above-mentioned storage capacitor 22, the primary winding 23, and the anodecathode circuit within discharge device 10. The discharge occurs only when the device is made conductive.

In order to make the disharge device conductive and discharge the storage capacitor through the device and the primary winding, an input transformer 28 has its primary winding connected to input terminals 30, 31, and its secondary winding 32 connected in series with a blocking capacitor 33 to the firing electrode 17. The other end of secondary winding 32 is connected to the cathode 16 and ground. The auxiliary anode 14a is connected to a resistor 34 whose other terminal is connected to the junction of secondary winding 32 and capacitor 33. The output transformer 24 has a secondary winding 35 which is connected to a load 36. This load may comprise a distributor and a plurality of spark plugs or it may be a flash lamp or any other type of circuit component which can use a series of voltage pulses.

The operation of this circuit is as follows:

Let it be assumed that at the start the storage capacitor is not charged and there are no potentials applied to any of the input terminals. First, a charging pulse is applied between terminals 26 and 27 and current flows through diode 25. and primary winding 23 to charge the capacitor 22. During this time the discharge device is nonconductive and no current flows through it. Now, a control pulse is applied across terminals 30, 31, which makes the control grid 17 positive and the tube 10 conducts, thereby discharging the electrical energy stored by capacitor 22. This discharge current passes through primary winding 23 and a high voltage is generated by secondary winding and applied to load 36. At the end of this discharge pulse the anode of the discharge device has its potential reduced to zero and then goes slightly negative due to the inductance and capacity in the discharge circuit. This portion of the operation is indicated by the graph in FIG. 4 where the line 40 represents the anode voltage before the discharge, line 41 represents the steep drop in voltage to zero during the discharge, and the negative spike 42 represents the negative potential assumed by the anode because of the resonant features in the output circuit. As soon as the discharge pulse is over, the potential applied to terminals 26, 27 causes a recharge of capacitor 22, this rise in voltage being denoted by curved line 43 in FIG. 4.

The voltage pulse applied to terminals 30, 31, generally assumes the shape of a sine wave by the time it is transferred through transformer 28 and blocking capacitor 33. Such an input pulse is indicated in FIG. 4 by the dotted line 44. It is obvious from the graph that the firing pulse 44 ordinarily consumes a time interval which is long enough to maintain the voltage of the firing electrode at a positive value so that (at high speeds) the anode voltage is made positive and the tube is fired a second time on the single input control pulse. Such a performance is undesirable and the operation fails.

In order to reduce the grid voltage 44 and produce a simple short firing pulse 45 the additional anode 14a is connected to the circuit. Now, when the anode voltage drops to zero, the cathode discharge is transferred to the auxiliary anode through insulator holes 20 and the ionized gases are removed from the space near the anode and the firing electrode 17. The potential of the auxiliary anode also drops to zero and then goes negative in a manner similar to the main anode.

When the auxiliary anode goes negative, it reduces the potential of the top end of the grid transformer secondary 32 to a low value and holds it there, thereby preventing any further buildup of potential on the firing electrode. Now, when the storage capacitor 22 is charged, there'will be no tendency for the discharge device to become conductive. It is to be understood that the curves shown in FIG. 4 represent very high speed operation and under normal circumstances the charging potential 43 would not reach its high value until after grid pulse 44 returns to zero.

While the above explanation is believed to be correct, further investigation may lead to a modification of this theory. It is to be understood that the invention is independent of any theory that may be advanced to ac- 5 count for the results obtained.

The foregoing disclosure and drawings are merely illustrative of the principles of this invention and are not to be interpreted in a limiting sense. The only limitations are to be deter-mined from the scope of the appended claims.

I claim:

1. A thyratron and circuit therefor comprising: a gaseous discharge device including a sealed envelope containing an anode, a cathode, a firing electrode, and an auxiliary anode positioned adjacent to the cathode and exterior to the space between the anode and cathode; a charging circuit which includes a source of electric power, a diode rectifier, a storage capacitor, and a coupling circuit connected to a load; a discharge circuit including in series said storage capacitor, said coupling circuit, and the anode-cathode circuit of said discharge device; a firing circuit which includes circuit means in series with a capacitor for impressing a positive voltage pulse upon the firing electrode of the discharge device; and an auxiliary anode circuit connected between the auxiliary anode and the cathode which applies a positive potential to the auxiliary anode after the device has been made conductive.

2. A thyratron and circuit therefor comprising: a gaseous discharge device including a sealed envelope contain-ing an anode, a cathode, a firing electrode, and an auxiliary anode positioned adjacent to the cathode and exterior to the space between the anode and cathode; a charging circuit which includes a pair of terminals for connection to a source of electric power, a diode rectifier, a storage capacitor, and the primary winding of an output transformer; a discharge circuit including in series connection said storage capacitor, said primary winding, and

the anode-cathode circuit of said discharge device; a firing circuit which includes an input transformer secondary winding connected across the cathode and the firing electrode in series with a blocking capacitor, said secondary winding adapted to transmit a positive pulse to the firing electrode; and an auxiliary anode circuit connected between the auxiliary anode and the junction of one end of said input Winding and one side of the blocking capacitor, said circuit for applying a positive potential to the auxiliary anode after the anode-cathode circuit of the device has been made conductive.

3. A thyratron and circuit as claimed in claim 2 wherein said output transformer has a secondary wind-ing c-0n nected to a distributor and a set of spark plugs.

4. A thyratron and circuit as claimed in claim 2 wherein said firing electrode is a hollow cylindrical conductor in axial alignment with the anode and cathode.

5. A thyratron and circuit as claimed in claim 2 wherein said firing electrode and said cathode are held in alignment by an insulator sleeve having a plurality of holes cut in the sleeve for providing a discharge path between the cathode and the auxiliary anode.

References Cited by the Examiner UNITED STATES PATENTS 2,362,937 11/1944 Shepherd 313-188 2,617,969 11/1952 Malter 313-188 2,635,810 4/1953 Townsend 313188 2,922,080 1/1960 Thomas 315340 3,032,684 5/1962 Kuykendall 315-483 3,032,685 5/1962 Loomis 315183 JOHN W. HUCKERT, Primary Examiner. I. D. KALLAM, Assistant Examiner. 

1. A THYRATRON AND CIRCUIT THEREFOR COMPRISING: A GASEOUS DISCHARGE DEVICE INCLUDING A SEALED ENVELOPE CONTAINING AN ANODE, A CATHODE, A FIRING ELECTRODE, AND AN AUXILIARY ANODE POSITIONED ADJACENT TO THE CATHODE AND EXTERIOR TO THE SPACE BETWEEN THE ANODE AND CATHODE; A CHARGING CIRCUIT WHICH INCLUDES A SOURCE OF ELECTRIC POWER, A DIODE RECTIFIER, A STORAGE CAPACITOR, AND A COUPLING CIRCUIT CONNECTED TO A LOAD; A DISCHARGE CIRCUIT INCLUDING IN SERIES SAID STORAGE CAPACITOR, SAID COUPLING CIRCUIT, AND THE ANODE-CATHODE CIRCUIT FOR SAID DISCHARGE DEVICE; A FIRING CIRCUIT WHICH INCLUDES CIRCUIT MEANS IN SERIES WITH A CAPACITOR FOR IMPRESSING A POSITIVE VOLTAGE PULSE UPON THE FIRING ELECTRODE OF THE DISCHARGE DEVICE; AND AN AUXILIARY ANODE CIRCUIT CONNECTED BETWEEN THE AUXILIARY ANODE AND THE CATHODE WHICH APPLIES A POSITIVE POTENTIAL TO THE AUXILIARY ANODE AFTER THE DEVICE HAS BEEN MADE CONDUCTIVE. 